After I mentioned that vegans must rely on fortified foods or supplements for vitamin B12, this person cited that fact as evidence that nature intends for humans to consume animals or animal secretions. This person's point had me incapable of responding. What is your take on this comment?I get this a question a lot, too, and there are a couple of ways to handle it. One is the way Jack Norris responded with, an entirely appropriate pointing-out that nature does not "intend" anything. In most cases, that suffices.
Problem is, it sometimes comes off as slightly dismissive, if not evasive. So, I have come up with another, equally valid response.
"B12 deficiency is a common problem even for meat-eaters. The Framingham Study determined that up to 40 percent of Americans have 'sub-optimal' B12 blood levels... and vegans are not 40 percent of America. So, it's a common dilemma, but fortunately, nature has engineered a way around it: the technical term is enterohepatic circulation. It's a mouthful, but all it really means is that once you have sufficient B12 stores, your body continuously recycles it through the bile system, keeping you at functional levels for years, sometimes decades. We should not rely on this by any means, but it's a fallacy to argue that because we need supplements or fortified foods to get B12, nature therefore 'intends' us to eat meat. Nature also engineered us to survive a long time without any external B12 sources. So the issue really comes down to ethics and free will, not the laws of nature."
I've tested versions of this response out on some evo-savvy interlocutors, and it works almost every time. For those who want evidence, I point out that the process is present in monkeys, indicating that enterohepatic circulation of cobalamin has likely been ancestral to our lineage since before the appearance of the Miocene "apes" about 22 Ma.
Having said that, though, I'm neither a doctor nor a dietitian, so turn to Jack Norris and Ginny Messina for any health-related questions.